Commercial food supplies for animals (e.g., birds, fish, cattle, etc.) consist of nutrients (e.g., protein, vitamins, minerals, fats, and carbohydrates), for example raw ingredients or food additives that may include whole, unprocessed food materials (e.g., meat or plants), marginally processed foods (e.g., fish meal, soy meal, nut meal, etc.), and waste by-products generated in the production of other food (e.g., wheat middlings, bone meal, blood meal, feather meal, etc.). One of the main motivations for employing alternative food additives in feed formulations is to reduce the cost of the protein component. Fish meal provides a common source of protein for animal food, particularly in the aquaculture, pig, poultry, and pet food industries. However, there are many drawbacks to the use of fish meal as a food additive. The continued growth of the demand for fish meal from global aquaculture operations places excessive strain on world fisheries, and may deplete wild fish stocks due to over-fishing. Several recent scientific journal and popular media articles point to an emerging consensus regarding decreased landings of wild fish, and the potential impending collapse of economically and ecologically vital fish stocks (see for example Watson and Pauley, Nature, vol. 414 (2001), pp. 534-536; Myers and Worm, Nature, vol. 423 (2003), pp. 280-283; and Special Report: The Global Fish Crisis, National Geographic, vol. 211. no. 4 (2007), pp. 32-99). In addition, seasonal fluctuations and meteorological events (e.g., El Niño, La Niña) influence market prices for fish meal.
Alternative by-product protein sources (such as bone, blood, and meat by-products) have been used in animal food industries in an effort to reduce reliance on fish meal as a protein source. However, there are concerns that such protein sources may compromise animal and human health, for example by causing the spread of “wasting” diseases, such as bovine spongiform encephalopathy (aka mad cow disease) and scrapie.
Vegetable products (such as soy and wheat) and monocultures (or well characterized mixed communities) of single-cell (i.e., microbial) protein sources have been evaluated as food additives. For example, microorganisms have been grown on substrates including natural gas (e.g., Norferm's currently abandoned Bioprotein® product, for example as described in U.S. Patent Publ. Nos. 2005/0124053 and 2005/0271771). Additional organisms that may be incorporated into animal food include algae, yeast, and zooplankton. An extreme example of alternative animal food sources is found in some developing-world aquaculture operations where the feces of pigs, ducks, cows, humans, and other animals have been utilized as a feed in order to recover the nutritional value remaining in these waste products. However, the use of such products as a feed may compromise animal (or human) health or impart an undesirable taste to the meat of animals fed in this manner.
Thus, raw material inputs for producing conventional animal foods draw from various sources, either directly from natural sources or derived as by-products from the manufacture of other food products. The incorporation of sufficient protein into the ultimate animal food is a major manufacturing goal, and greatly influences the total cost of producing animal feedstocks. Increasingly, food producers, particularly in the aquaculture and domesticated animal food industries, have utilized fish meal harvested from various natural fisheries. However, this dependence has led to concerns about the depletion of natural resources.
As discussed above, animal foods can be supplemented with waste-by-products derived from the production of human or animal foods or ingredients for animal or human foods. The term “human or animal foods” includes any food or beverage for human or animal consumption, as well components of human or animal foods (e.g., corn syrup, molasses, etc.). Food production processes can produce waste streams containing “solid matter residuals” (i.e., solid waste streams) or “waterborne residuals” (i.e., dissolved and particulate waste matter entrained in water). When by-products are used in the production of another salable product (such as animal feed), the process is commonly referred to as co-production. For example, fish meal is the product of processed whole food (school fish such as menhaden, anchovies, sardines, etc.) or food processing residuals (fish heads, bones, internal organs), while wheat middlings (a solid matter residual) are a co-product food additive which can be used as an ingredient in animal food. Further examples of solid matter residuals used in animal foods include waste hops, barley, and yeast from breweries (e.g., for cattle, horses, and chickens).
Waterborne residuals are generally treated in wastewater treatment plants, where contaminants from the aqueous waste streams (i.e., wastewater) are removed prior to the ultimate disposal of the treated waste water in a receiving water body or another wastewater treatment plan (e.g., a river or a larger wastewater treatment plant). Waterborne residuals can also be subjected to pretreatment in which the wastewater producer partially treats the wastewater to remove at least a portion of the waterborne residuals prior to sending the wastewater to another wastewater treatment plant (e.g. a municipal wastewater treatment plant). Wastewater can derive from industrial processes (such as a food processing facility, where sewage inputs are not necessarily present) and domestic sources (such as a municipality, where sewage inputs are primary contributors to overall flow). The most common contaminants present in wastewater include soluble, carbon-containing (i.e., organic) compounds that contribute to biochemical oxygen demand (BOD). BOD is a measure of the oxygen required for biological degradation of the contaminants in water or wastewater and is generally correlated to the amount of waterborne organic material contained in that wastewater. In other words, the greater the organic matter content of a wastewater, the greater will be the BOD level determined for that wastewater. In order to meet most regulatory standards in the United States, BOD levels should generally fall below about 30 mg/L prior to discharge to a receiving water body. Influent wastewaters to wastewater treatment plants may vary greatly with regard to their BOD concentrations and biochemical characteristics. For example, food-producing facilities may generate wastewaters containing BOD levels in excess of 30,000 mg/L while wastewater treatment plants processing municipal sewage generally receive wastewater averaging between approximately 200 mg/L and 400 mg/L. Furthermore, wastewater may contain BOD-contributing compounds having a wide range of chemical structures and molecular weights.
Many wastewater treatment processes rely upon the biological conversion of a BOD substrate into a cellular mass. In some cases—particularly in the food industry—biological treatment processes may prove difficult to implement as the result of nutrient limitations (e.g., due to the presence of nitrogen, phosphate, or some other essential nutritional component in concentrations insufficient to promote the balanced growth of microbial cells). Balanced growth in bacteria means that sufficient quantities of nutrients are both present and biologically available at the time that the organisms in the organic substrate come into contact. The simultaneous presence of substrate and nutrients allows bacteria to produce the molecular components most generally associated with cellular growth, specifically protein, nucleic acids, and lipids. When sufficient quantities of nutrients (including both so-called “macronutrients” such as nitrogen and phosphorus, and so-called “micronutrients” such as metals and vitamins) are not present, bacteria experience non-balanced growth. In contrast to balanced growth, non-balanced growth is characterized by the increased production of polysaccharide material about the cell—a process by which carbon atoms are sequestered away from the molecules involved with cellular growth (e.g., proteins, nucleic acids, and lipids).
FIG. 1 provides a schematic for a typical type of wastewater treatment plant using a biological treatment process. Influent wastewater containing food byproducts 1 is introduced to the treatment process (FIG. 1). Although plant designs may vary, the essential biological wastewater treatment process involves contacting microorganisms (especially bacteria) with waterborne organic material (i.e., BOD) in the wastewater. Commonly, this contact occurs in an aeration basin (or series of basins) 4 in which oxygen is introduced to maintain aerobic conditions. The microorganisms metabolize the waterborne residuals contained in the wastewater, thereby utilizing available energy (in the form of reduced carbon compounds) contained therein. In the process of meeting cellular metabolic needs, including maintenance and growth (i.e., cellular proliferation), residual matter (i.e., BOD-contributing compounds) in the wastewater is metabolized and converted into microbial mass. In order to separate treated water from this solid microbial mass (aka solids), the contents of the aeration basin(s) 4 can be allowed to settle in a clarifier basin 5 (it will be understood that other types of separation equipment could be substituted for a clarifier basin). A portion of the separated solids (i.e., containing bacteria) 7 is then returned to the aeration basin(s) 4 to maintain a high concentration of organisms therein. In order to maintain quasi-steady state conditions, those solids not returned to the aeration basin must be “wasted” (i.e., removed) 8 from the treatment process. These wasted solids are commonly referred to as waste activated sludge (WAS). Therefore, as a result of biological wastewater treatment processes, the aqueous residuals (i.e., BOD-contributing compounds) in the influent wastewater stream are largely incorporated into cellular solids that ultimately must exit the treatment process while the treated water 6 (with greatly reduced BOD levels) is discharged to a receiving water body. Removed cellular solids (i.e., WAS) are collected and disposed of in a variety of ways, most commonly after partially removing the intracellular water (i.e., dewatering) in a dewatering process.
FIG. 2 outlines one conventional process for dewatering and disposal of this cellular material. Waste solids 15 are applied to a belt filter press 16 that partially removes the intracellular water contained therein. This method of dewatering is one of several conventional methods, which can include centrifugation, drying, various types of filter presses, etc. Upon introduction to the belt press, the solids content in WAS is often less than approximately 3% solids on a percent by weight basis. However, at the completion of belt-press dewatering, the solids content in the resulting filter-cake (comprised of partially dewatered biological solids, aka biosolids) 17 is often between about 15% and about 20% solids. The intracellular water removed during dewatering (i.e., filtrate) is normally returned to the wastewater treatment process 18. The partially dewatered solids must then undergo a solids disposal process 19. These disposal options are generally costly to the producer of the biosolids material, primarily due to the high cost of transportation and tipping. As a result, biosolids producers often process the biosolids before and after dewatering to decrease the volume of material for disposal. Such processes include aerobic and anaerobic digestion—to convert particulate carbon matter (i.e., solids that would otherwise require disposal) to gaseous forms such as carbon dioxide and methane. These volatile components may be either released directly to the atmosphere or burned, thereby decreasing the amount of solids material requiring disposal. Other processes for decreasing the quantity of biosolids requiring dewatering include anaerobic biological treatment processes in which decreased cellular material is produced from the energy-containing BOD.
Other alternatives for disposing of biosolids from wastewater treatment plants (i.e., WAS) include ocean dumping, incineration, land-filling, and land-application. However, ocean dumping has become increasingly more regulated and costly due to concerns about contaminating the environment. Similar concerns have led many wastewater treatment plants to move away from WAS incineration due both to regulatory concerns and to the high energy input required. Land-filling of WAS is also problematic since most facilities will not accept wet matter. Likewise, land-application of WAS can engender strong community resistance and strict regulatory controls due to concerns over pathogenic organism dispersal (for example, regulatory requirements for composting processes require careful temperature monitoring to ensure de-activation—i.e., killing—of the microorganisms comprising the biosolids).
Due to these concerns, the composting of biosolids has become a more attractive method for disposing of waste microorganisms derived from wastewater treatment processes. As a result of proper implementation of composting procedures, wastewater treatment plants may even be able to generate modest incomes by selling compost material (generally referred to as “Class A biosolids” see 40 C.F.R. §503). Alternatively, thermally dewatered biosolids have also been sold as fertilizers and soil conditioners (e.g., Milorganite® fertilizer and soil conditioner, a product manufactured by the Milwaukee Metropolitan Sewerage District).
U.S. Pat. No. 4,119,495 describes extracting protein from hydrolyzed WAS to provide a nutrient source for culturing other microorganisms, such as yeast, or as a protein additive for feeding animals. However, this process involves costly pH and temperature adjustments in order to recover microbial protein. Other researchers have evaluated using the activated sludge component from domestic wastewater treatment processes as a foodstuff, but as yet no large-scale commercial process for so doing has been implemented (Anwar et al., Aquaculture, vol. 28 (1982) pp. 321-325; Tacon and Ferns, Agriculture and Environment, vol. 4 (1978/1979) pp. 257-269; Tacon and Ferns, Nutrition Reports International, vol. 13 (1976) pp. 549-562; Tacon, Proc. World Symp. On Finfish Nutrition and Fishfeed Technology, Hamburg 20-23 Jun. 1978, Vol. II. Berlin 1979; Edwards, 1992, Reuse of Human Wastes in Aquaculture: A Technical Review, UNDP-World Bank Water and Sanitation Program).